Cells in a variety of contexts migrate towards soluble chemical cues in a process known as chemotaxis. Despite nearly a century of study, the mechanistic underpinnings of chemotaxis remain incompletely understood. Spatial gradients of growth factors direct the movements of mesenchymal cells in tissues to coordinate and accelerate physiologically important processes such as wound healing, and mesenchymal chemotaxis has been implicated in pathological conditions such as cardiovascular and fibrotic diseases. Yet, the vast majority of chemotaxis studies have focused on leukocytes and other fast-moving, amoeboid cells. Mesenchymal chemotaxis has been prohibitively difficult to study, because it requires maintenance of stable gradients for many hours. Traditional methods such as transwell assays provide little or no dynamic information and poorly discriminate effects on the efficiency of motility from actual directional sensing. To overcome these technical limitations we recently established a microfluidic chemotaxis assay that allows direct observation of mesenchymal cells in stable, linear gradients over many hours, allowing both single-cell tracking and high-resolution live-cell imaging approaches such as TIRF microscopy. Our preliminary data indicate that the growth factor receptor, PDGF-R controls mesenchymal chemotaxis by a PLC > PKC > Myosin II pathway and requires the coordination of signaling events and cytoskeletal organization. We propose to elucidate the mechanisms of mesenchymal chemotaxis by 1) Dissecting the spatio- temporal nature of chemotactic signaling in mesenchymal cells 2) Understanding the dynamic organization of the cytoskeleton during chemotaxis in this cell type and 3) Delineating the coordination of signaling and cytoskeletal events that lead to complex chemotactic behaviors such as re-orientation to new cues and chemotaxis in 3D environments. These studies will directly contribute to our understanding the physiological basis of disease states such tumor metastasis, fibrosis and cardiovascular disease, as well as our understanding of physiological processes such as wound healing.